This is the painting that signposted the way to the future for the great American modernist Mark Rothko. The painter's simple but subtle stripes of colour became a trademark in later years, but this work, White Center (Yellow, Pink and Lavender on Rose), was the first of its kind, writes Vanessa Thorpe

On Tuesday Sotheby's in New York will sell the groundbreaking picture from 1950 for an estimated £20m when private bidders from across the world are expected to vie to own one of the most important artistic experiments of its era.

The picture has not come up for auction before and was a favourite of Peggy Rockefeller, the wife of David Rockefeller, the banker and philanthropist who has owned the painting since 1960. 'This wonderful painting has given me great pleasure for almost 50 years,' Rockefeller said in the run-up to the sale this week. He hung the work outside his New York office after being initially persuaded to buy it by Dorothy Miller, the famous Chief Curator of New York's Museum of Modern Art.

'I hope another admirer of abstract expressionism will derive similar pleasure from it,' he added.